Taped plastic balloon



Nov. 5, 1963 J. A. WINKER ETAL 3,109,612

TAPED PLASTIC BALLOON Filed May 9, 1962 INVENTORJ' Jena: :5, M72262)" BY Paul 15 V052 United States Patent 3,1tl9,612 TAPED PLASTIC BALLOUN James A. Winlter and Paul E. Yost, Sioux Falls, 5. Dale, assrgnors to Raven industries, lino, Sioux Falls, S. Dale, a corporation of South Dakota Filed May 9, 19:52, Ser. No. 193,375 2 Claims. {(Il. 244-61) The present invention relates to improvements in load carrying balloons and particularly to animproved structure for the attachment of load lines to a load carrying balloon envelope.

The use of plastic material has made it possible to use lightweight thin plastics for balloons which are capable of carrying very heavy loads. The lightweight thin balloon material can successively carry a heavy pay load into the stratosphere without damage to the balloon material because of the distribution of the forces of the weight of the pay load over the surface of the balloon envelope, and in the design of balloons for heavy loads the chief technical problem is obtaining requisite balloon strength. A standard procedure has been to seal load tapes to the surface of the balloon material to act as a net, absorbing the load in fittings at the base and at the top of the balloon. During the floating period of balloon flight, after launching, the shape of the balloon is well known, and maximum utilization can be made of the strengths of the load tapes and the film which provides the balloon material. Very heavy loads on the order of 5,000, 10,000 or even 20,000 pounds can be carried 'With such balloon designs.

The factors encountered during launch and ascent hoW- ever are quite different than during normal flight and unequal or preferential loadings can occur which will exceed material strengths. These loadings will naturally occur in the bubble area of the balloon envelope and may be either in the pressured upper regions or in the sub-pressure area on the underside of the bubble. As will be appreciated by those versed in the art, these heavy load carrying balloons are usually formed of a thin plastic material such as polyethylene which is shaped in gores with the gores attached to adjacent gores at their edges by seams to form the overall balloon envelope having the natural shape wherein no lateral stresses are present in the inflated floating balloon. At launching however a small bubble of gas will be formed in the upper end of the balloon and this bubble will expand at high altitudes to inflate the balloon. It is of course possible to reinforce the portion of the balloon envelope, which will be the bubble portion at launching, to enable carrying greater loads. At floating altitude, a properly designed and taped natural shape balloon will be fully inflated, and near the base all the stresses will be in the tapes and will be meridianal. In a wide region above and below the equator of the balloon the load will have transferred almost entirely into the film and inasmuch as the balloon is natural shaped, the stresses will remain entirely in the vertical direction. As the material width diminishes near the top the load will be transferred back to the tapes and again must be meridional. Here, however, the natural shape principle is violated in part because of the concentration of load at regular radial intervals. The pressure of gas against the film in the upper regions is not counterbalanced by the theoretical meridional force and therefore bulging or doming between the tapes tends to occur.

Transverse stressing also occurs in this upper area, but with the proper allowance of excess material the balloon skin can bulge to a small radius of curvature relieving this transverse stress to a readily acceptable value. For example, a 4,000,000 cubic foot balloon carrying a load of 8,000 pounds will float at about 80,000 feet. If 5% excess material is allowed in the gore width, the radius 3 ,lfl9,h l2 Patented Nov. 5, 1963 of curvature of the material between the tapes will be equivalent to the gore width. At a point where the balloon contour begins to deviate from; the .nearly flat top, gore Width is 40". At floating altitude, pressure on the upper balloon skin is .46 psf. or .0032 p.s.i. Thus if no meridional stress remains, which is probably not the case, the stress is:

St==Pr=.0032 X 40:.128 lb./inch This, of course, is tolerable by even the thinnest balloon films.

The loading, per tape, near the apex is:

L see. 6/2-l-balloon wt. 8000 1.77-i-l000 n 81 With a nominal 5:1 safety factor, 1000 pound load tape is more than adequate. Clearly, both vertical and horizontal loads are well within material limitations on a floating balloon carrying loads up to many tons.

As stated above, it is during the launch and ascent portion of the flight that critical stresses might arise and it must be assumed that these are the result of the transfer of load from tape to film. Because of the immense amount of uninflated film in a balloon at launch, it is inevitable that the balloon will take a configuration including folds, gathers and convolutions. The load tapes, following these twists and gathers, will have diiferent path lengths with the result that there will be different loading among them. It has been noted in most inflated balloons that /2 to /3 of the tapes in the smooth part of the bubble are more or less uniformly loaded, while in the remainder the load varies down to Zero. in the absence of a cone angle in the balloon envelope, the uniformly loaded tapes should carry the pay load with the same safety factor as experienced at floating altitude.

The critical stress problem then resolves itself to one of shear loading in the film between tapes under different stress. This may generally be observed in balloon bubbles as stress wrinkles at various angles between gores. During launch or ascent this shear could easily exceed material strengths and this is very likely the cause for many of the failures of heavy load balloons.

It is accordingly 2. primary object of the invention to provide an improved balloon structure which eliminates shear loading on the balloon film from the tapes to thus avoid excessive shear stress during launching and ascent.

In accordance with the principles of the present invention, shear loading on the film is eliminated by using a load member in the form of a vertical load line or load tape which is not restricted in its movement relative to the material of the balloon envelope and is not intimately or rigidly attached to the balloon surface. The load mem bers or load lines must necessarily be held captive to the balloon to retain their relative orientation but the balloon body should be allowed to have freedom of movement in a vertical direction relative to the load lines.

In accordance with one arrangement the invention contemplates provision of load lines which are enclosed in sheaths or tubes extending vertically which limit the lateral movement of the load line but permit maximum vertical movement. The enclosure for the load lines may be in the form of a separate piece of tubing attached to the balloon envelope and extending parallel to the load line; may be in the form of 'an extension of the gore projecting outwardly beyond the seam; or may be in the form of loops encircling the load line or of other constructions. In a further arrangement the load line may be attached some distance from the balloon surface by means of a flexible linkage which allows approximately equal lateral and vertical movement, and this may be provided in the form of a Web of lightweight polyethylene; or in the form i of tie lines or other methods of attachment.

It is accordingly a further object of the invention to provide an improved belloon construction wherein load members are supported on a balloon envelope substantially free of vertical restriction with respect to the material on the surface of the balloon envelope so that relative shifting can occur preventing the transferral of shear stresses to the balloon material.

A further object of the invention is to provide a balloon envelope with vertically extending load lines having means for retaining the position of the load lines relative to each other in the lateral direction permitting vertical slippage between the surface of the balloon material and the load lines.

A still further object of the invention is to provide an improved tubular sheath construction for a balloon envelope for retaining the lateral orientation between load lines.

A further object of the invention is to provide a linking connection between the surface of a balloon envelope and load lines which is yieldable in a vertical direction to prevent the transferral of film damaging stresses due to shifting or extension of load lines.

Other objects, advantages and features will become more apparent with the teaching of the principles of the invention in connection with the disclosure of the preferred embodiments thereof in the specification, claims and drawings, in which:

FIGURE 1 is a side elevational view of a balloon in flight illustrating .an overall balloon construction of the type embodying the principes of the present invention;

FIGURE 2 is a diagrammatic illustration showing the transferral of shear stresses to balloon envelope film in a conventional construction;

FIGURE 3 is an enlarged vertical sectional view taken substantially along line III-Ill of FIGURE 1 providing a detailed illustration of the structural relationship between load members and the balloon envelope;

FIGURE 4 is a fragmentary perspective view of a portion of a wall of the balloon envelope showing the structural relationship between the load line and balloon envelope;

FIGURES 5 through 7 are horizontal sectional views similar to FIGURE 3 and illustrating other structural relationships between load lines and the balloon envelope; and

FIGURE 8 is a perspective view of a portion of a wall of the balloon having a construction such as illustrated in FIGURE 7.

As shown on the drawings:

FIGURE 1 illustrates a balloon envelope '10 formed of a balloon material arranged in vertical gores 12. The gores are attached to each other at seams which are shown at the same location as vertical load carrying members 15 attached at their upper ends to a suitable interconnecting fitting 13 and at their lower ends to a fitting 14 which is suitable for attachment to a pay load 11. The load carrying members 15 will be for purposes of convenience referred to as load lines or load tapes. It should be made clear however that they do not have the relationship to the balloon of conventional tapes which are heat sealed or otherwise secured to the balloon envelope film.

FIGURE 2 illustrates load tapes 17 of conventional design which are conventionally attached to the film 16 by heat seals or adhesives. The forces of the gas on the film shown at S are transmitted in the film to the seam beneath the tape 17. Because there is excess circumferential material there is no circumferential stress because of circular tightness, but the stress results because of opposing tape and film forces. These resolve largely into opposite vertical stresses or shear stresses between tape and film. These stresses are avoided with the arrangement of the present invention.

FIGURE 3 shows the balloon gores 12 joined to each other along the seam S. Extending vertically along the seam is a sheath or tube 18 formed of a convenient 4 exible material such as polyethylene. This sheath is sealed to the balloon in a convenient manner such as by fastening strips Zll sealed at one end to the sheath, and at the other end joined to the balloon envelope material by a joining seam 21.

The sheath contains the load carrying member or load line 19. The load line may take various forms suitable for carrying the weight of a pay load, and in one form may incorporate individual fibers or filaments in roving form. In other words, the filaments are not attached to each other but are individual filaments which can slip relative to each other and are held together by the sheath 1%. The fibers for the load line 19 may be of various materials such as nylon, fiberglass or Dacron or similar materials. Fortisan fibers have been found to be advantageous, and the quantity and size of the fibers will depend on the load to be carried by the balloon and the optimum rated strength can be calculated for any given pay load and balloon combination. The fibers are suitably attached at the upper end of the balloon and atthe lower end by conventional end fittings presently in use, such as clamp type fittings.

The material chosen for the load line 19 is preferably slippery relative to the material of the sheath, or to the material of the balloon envelope if a discontinuous sheath or separated loops are used for the load lines. The friction of F ortisan against polyethylene is quite low and will readily allow slippage to relieve local shear stress concentration.

FIGURE 5 illustrates another arrangement wherein balloon gores 22 and 23 are joined to form a seam 24 and the balloon film material projects out beyond the seam 24. Attached to the extra material is a loop 23 to form a tubular sheath for a load line 29 and the sheath is attached to the extensions 26 and 27 of the gores by a suitable attachment 3%). The load line 29 is enclosed within the sheath 23 and is shown as a fiat tape and of course other load line formsmay be employed.

FIGURE 6 illustrates the material of the balloon itself used to provide a sheath, and the gores 31 and 32 are joined at a seam 33, with portions 34 and 35 extending outwardly of the seam and joined at 37. They thus form a sheath or pocket for containing the load line 36.

FIGURES 7 and 8 illustrate an arrangement wherein a load line 39 is attached to the balloon envelope material by a flexible link in the form of a shear web 4th The web 40 is attached at its inner edge lba by a seam 41 to the balloon material, and at its outer edge 40b to the load line 39. The shear web 44 and line 3? are on the exterior of the ballon envelope as are each of the load line arrangements shown.

A preferred form of shear web 49 would be on the order of 4" wide and of a material preferably of less strength than the gore material. For example in a polyethylene balloon of 1 mil thickness, a shear web of mil would be employed. Similarly for a 2 mil balloon a shear web of 1 mil may be employed. The shear web provides an excellent stress absorbing member, alleviating most of the stresses normally transmitted directly into the balloon film, and yet functions to maintain the lateral orientation of the load lines. If the stresses are exceedingly severe, the shear web 40 acts as a sacrificial link and will rupture before the material of the balloon ruptures but the balloon will still perform its mission satisfactorily.

In summary, as illustrated in FIGURES 3 and 4, at tached outwardly of the balloon envelope material 12 is a tubular sheath 1% which retains the horizontal or lateral orientation of the load line 19 but permits slippage of the load line vertically therein, or relatively vertically with respect to the balloon envelope material 12. This construction avoids the normal integral tape and envelope construction and in effect provides a tapeless construction, which provides a substantial advantage in that any tendency toward localized stress concentration is automatically relieved as the amorphous nature of the balloon allows the material around the area of the tape to stretch and relax. This construction combines the best features of a tape balloon, and a conventional tapeless balloon provided with no load lines, in that strong fibers are still employed to support the pay load but the balloon material is sufiiciently unrestrained to stretch and relax and take a configuration of minimum stress.

The drawings and specification present a detailed disclosure of the preferred embodiments of the invention, and it is to be understood that the invention is not limited to the specific forms disclosed, but covers all modifioations, changes and alternative constructions and methods falling within the scope of the principles taught by the invention.

We claim as our invention:

1. A load carrying balloon comprising a balloon envelope for containing a lifting gas, a plurality of downwardly extending load lines adapted for connection to a pay load below the balloon and connected above the halloon for transferring the weight of the pay load to the 20 ballon envelope, and webs extending along the load lines each attached along one side to said balloon envelope and attached along the other side to the load line permitting vertical shifting of the load lines relative to the balloon material, said webs being formed of a material having less strength than the material of the balloon envelope.

2. A load carrying balloon comprising a balloon envelope for containing a lifting gas, said envelope formed of a plurality of gores of thermoplastic material, portions at the edges of the gores turned outwardly and having continuous gas impervious heat weld seams formed between said portions inwardly of the outer edges with the outer edges projecting outwardly of the seam, stitching joining the outer edges to form a sheath between the seam and stitching with said stitching forming an air and gas pervious juncture permitting expansion and contraction of the sheath and permitting the escape of vapor therefrom, and a load line extending through said sheath.

Sturtevant May 25, 1954 Winzen Nov. 15, 1960 

1. A LOAD CARRYING BALLOON COMPRISING A BALLOON ENVELOPE FOR CONTAINING A LIFTING GAS, A PLURALITY OF DOWNWARDLY EXTENDING LOAD LINES ADAPTED FOR CONNECTION TO A PAY LOAD BELOW THE BALLOON AND CONNECTED ABOVE THE BALLOON FOR TRANSFERRING THE WEIGHT OF THE PAY LOAD TO THE BALLOON ENVELOPE, AND WEBS EXTENDING ALONG THE LOAD LINES EACH ATTACHED ALONG ONE SIDE TO SAID BALLOON ENVELOPE AND ATTACHED ALONG THE OTHER SIDE TO THE LOAD LINE PERMITTING VERTICAL SHIFTING OF THE LOAD LINES RELATIVE TO THE BALLOON MATERIAL, SAID WEBS BEING FORMED OF A MATERIAL HAVING LESS STRENGTH THAN THE MATERIAL OF THE BALLOON ENVELOPE. 